The
term "Global Positioning System", often shorted to
"GPS", refers to any system which positions the
location of the observer anywhere in the world. Such "Where
Am I?" systems have been around for a while, and here's how
they work:

GPS
works by there being a number of satellites in orbit, and as
they all know where they are precisely, and they
know what time it is precisely, they can
transmit that information. Then, because radio waves travel at
the speed of light, which is
known precisely, it's possible for the GPS unit to work out
precisely where it is, and to tell you. (In effect it's advanced
radio trigonometry).

A
basic GPS box can tell you your exact Latitude and Longitude, and
to some extent your Altitude. (Curiously, it can also tell you what time it is!). However, GPS has come a long way
since it began, and there are a multitude of GPS add-ons or GPS Plus gadgets
and applications which include Sat-Nav (and all
the problems that go with that!).

The
first form of conventional portable sat-nav that worked globally
was the Early GPS Global
Positioning System. This was put up by
the United States, initially
as a military navigation system. However, it soon proved so
useful for civilian purposes that it became "The GPS",
and had widespread use globally. It had many things going for it,
but had an unfortunate built-in error in the location, which it
has been speculated was put in so that enemies of the USA would
not be able to use the US-made GPS against its forces! Incidentally, there is a Russian GPS which is Glonass.

Following on from the success of the
earlier American system, mainly
for civilian purposes, people in Europe found that they required a higher
accuracy precision Global Positioning System. The first satellites for Galileo went up
and went on test. However, this was not well met by the military
in the USA, who realised that Galileo could be used by anyone
anywhere in the world, and could in theory be used in battle
against US forces. So, the USA insisted on NATO having the
capability to jam Galileo. (It is rumoured that the USA
threatened to shoot it down if they weren't given that power).

With
the continuing move towards open standards and freedom of use of
technology anywhere without let or hindrance, as per Linux, it is
hoped that someone puts up an additional system that can't be
jammed by anyone. This would be Pure GPS, a system
that everyone can use and everyone can rely on, and without fear
of it suddenly being cut off.